A digital oscilloscope samples analog signals at a very high rate and stores the data in a RAM buffer for display on a display screen. In some architectures, a dedicated data acquisition subsystem acquires the data, and a display subsystem hosts the user interface and displays the data to the user. In these architectures, the display subsystem may be hosted by a standard personal computer, while the digital data acquisition subsystem may be an external module or “black box” connected to the personal computer via a high-speed communications link.
In a typical display subsystem, a large buffer size allows a large number of samples to be stored, which provides more details for display, such as for a “data zooming”feature. Generally, these architectures tradeoff the number of samples transferred to the display subsystem against display refresh rate. For example, if a very fast communication link is used, such as USB 2.0 “high speed,” a large number of samples can be transferred at an acceptable rate (e.g. 500,000 samples of 16 bits at 10 waveforms per second). Unfortunately, high-speed data transfer requires expensive components and commensurately high processing power on the display subsystem. Conversely, if a moderate or slow speed communication link is used, such as, for example, USB 1.1 or USB 2.0 “full speed,” RS-232, WiFi, Bluetooth, etc., the number of samples that can be transferred at an acceptable refresh rate is much more limited, and data may not be acquired, transferred and displayed at the desired rate.
Furthermore, a typical application of a digital oscilloscope is the detection of an irregularity in a train of pulses. Such irregularity, usually called a “glitch,” can consist of a missing pulse or an extra pulse or a bad shaped pulse. In a vehicular diagnostic context, pulse trains may include injector pulses, primary ignition pulses, phase sensors, TDC sensors, as well as many others. Usually, a glitch in these signals indicates a malfunction. Such failures are often sporadic and difficult to detect, as they may appear only at specific speed or load conditions. The ability of the digital oscilloscope to detect and capture glitches, while minimizing false alarms, is therefore important in order for the diagnostic process to be useful. One of the problems that affect current devices is the difficulty associated with changes in frequency, which is a normal behavior of the signal in case of accelerations or decelerations.
Accordingly, it is desirable to provide a digital data acquisition module that maintains provides improved glitch detection, full zooming capabilities and a fast refresh rate while operating over a slow or moderate speed communication link.